The technical field of the invention is Q-switched lasers and, in particular, pulsed lasers having a capacity for adjustable pulse duration independent of repetition rate.
Conventionally, Q-switched lasers employ solid state crystals or other gain media within a cavity to modulate laser resonance. The gain medium stores the energy until a triggering signal or other threshold event causes the energy to be released as a large pulse. For example, the medium or switch can be an acousto-optical or electro-optical crystal which switches the "Q" of the cavity between a high value which supports lasing action within the resonant cavity and a low value which essentially turns off the resonant cavity. While the switch is turned off, the pumping energy builds a population inversion within the cavity. When the Q-switch is turned on, the built-up population inversion is rapidly discharged, resulting in a large pulse of laser energy.
In such conventional Q-switched laser systems, there is typically little or no control over pulsewidth. The pulsewidth is largely dependent on the cavity, itself, and the switching repetition rate. Moreover, conventional Q-switched laser systems are often ill-suited for production of very long laser pulses, e.g., on the order of 10 milliseconds or longer.
There exists a need for variable pulse width lasers, particularly in the medical, communications, and radar fields. Laser surgical systems, in particular, could benefit greatly from a simple laser control system which permitted the user to modify the pulsewidth of therapeutic laser radiation during a surgical procedure. As lasers become more commonplace in medical therapy, it is becoming apparent that different biological structures (e.g., bone and other hard materials versus soft tissue) can be ablated optimally with laser pulses of different peak powers and/or durations. Similarly, non-ablative procedures, such as tissue fusion or suturing, can be performed optimally in yet another pulse mode regime.
Accordingly, a variable pulse width laser system, permitting the operator to modify the pulse widths from about 1 microseconds or less to 10 milliseconds or more, would satisfy a long-felt need in the art.